Browsers such as Chrome and Firefox apply an arbitrary scale to the
current font size if `normal` is used for `line-height`. Firefox uses
1.2 while Chrome uses 1.15. Let's go with the latter for now, it's
relatively easy to change if we ever want to go back on that decision.
This also requires updating the expectations for a lot of layout tests.
The upside of this is that it's a bit easier to compare our layout
results to other browsers', especially Chrome.
- Change min track sizing function to be "auto" when flex size is
specified.
- Never check if min track sizing funciton is flexible, because only
max is allowed to be flexible.
- Address FIXME in automatic_minimum_size to avoid regressions after
making two fixes mentioned above.
